Microdialysis technique has been developed to measure neurotransmitters in the rhesus monkey brain. This technique would help characterize the neurochemical and neuropharmacological correlates of frontal and temporal lobe function. Extracellular dopamine levels were detected not only in the caudate nucleus, but also in the prefrontal cortex. Dopamine levels in cortex were much lower than in the caudate. Dopamine was consistently found in the neostriatum and levels dramatically increased when amphetamine or cocaine were infused through the dialysis probes. The increase was demonstrated in the cortex even when prior to the amphetamine or cocaine infusion the baseline dopamine levels were not consistently detected. Consistently significant changes were noted in the cortical and striatal dopamine levels following infusion of calcium free cerebrospinal fluid, amphetamine or cocaine in the sedate monkey. Systemic administration of amphetamine and cocaine also resulted in changes in dopamine release in the extracellular compartment. The guide cannula system which aids in the accurate and repeatable placement of probes has proven to be strong enough to be used in the awake behaving monkey. Our long term goal is to correlate the baseline neurotransmitter levels to performance on specific behavioral tasks and we plan to manipulate the transmitter levels using relevant agonists and antagonists and observe changes in cognitive performance.